Technical Field
This application relates to a vascular filter and more particularly to a vein filter for capturing blood clots within the vessel.
Background of Related Art
Passage of blood clots to the lungs is known as pulmonary embolism. These clots typically originate in the veins of the lower limbs and can migrate through the vascular system to the lungs where they can obstruct blood flow and therefore interfere with oxygenation of the blood. Pulmonary embolisms can also cause shock and even death.
In some instances, blood thinning medication, e.g. anticoagulants such as Heparin, or sodium warfarin can be given to the patient. These medications, however, have limited use since they may not be able to be administered to patients after surgery or stroke or given to patients with high risk of internal bleeding. Also, this medication approach is not always effective in preventing recurring blood clots.
Therefore, surgical methods to reduce the likelihood of such pulmonary embolisms by actually blocking the blood clot from reaching the lungs have been developed. To this end, minimally invasive surgical techniques have been developed involving the placement of a mechanical barrier in the inferior vena cava. These barriers are in the form of filters and are typically inserted through either the femoral vein in the patient's leg or the right jugular vein in the patient's neck or arm under local anesthesia. The filters are then advanced intravascularly to the inferior vena cava where they are expanded to block migration of the blood clots from the lower portion of the body to the heart and lungs.
These prior filters take various forms. One type of filter is composed of coiled wires such as disclosed in U.S. Pat. Nos. 5,893,869 and 6,059,825. Another type of filter consists of legs with free ends having anchors for embedding in the vessel wall to hold the filter. These filters are disclosed, for example, in U.S. Pat. Nos. 4,688,553, 4,781,173, 4,832,055and 5,059,205, 5,984,947 and 6,007,558. Another type of filter is disclosed in U.S. Pat. No. 6,214,025 consisting of wires twisted together to form a cylindrical anchoring portion conforming to the inner vessel wall surface to exert a radial force and a conical filtering portion.
Several factors have to be considered in designing vein filters. One factor is that the filter needs to be securely anchored within the vessel wall, while avoiding traumatic engagement and damage to the wall as well as damage to the neighboring abdominal aorta. Another factor is that the filter must be collapsible to a sufficiently small size to be easily maneuvered and atraumatically advanced intravascularly to the inferior vena cava or other target vessel. Thirdly, the filter should direct the blood clots to the center of the vessel to improve dissolution of the clot within the vessel by the blood flow.
The filters disclosed in the commonly assigned co-pending application Ser. No. 10/889,429 (hereinafter “the '429 application”), the entire contents of which are incorporated herein by reference, satisfy the foregoing parameters. The filters have sufficient anchoring force to retain the filter within the vessel while providing atraumatic contact with the vessel wall, have a minimized insertion (collapsed) profile to facilitate delivery through the vascular system to the surgical site, and direct migration of the captured blood clots to the center of the vessel. The filters also provide simplified insertion through the femoral or the right jugular vein or arm into the inferior vena cava.
The filters of the '429 application can advantageously be readily removed minimally invasively, e.g. intravascularly, from the patient, thus advantageously providing for a temporary filter. Thus, these filters advantageously strike the balance of having structure to provide sufficient anchoring while enabling atraumatic removal from the vessel after a period of time. Certain filters of the '429 application also advantageously have a retrieval end configured to facilitate grasping by a snare as well as to facilitate withdrawal by providing a smooth transition into a retrieval sheath.
The filters of the '429 are very effective in achieving their desired functions, whether used as a permanent or temporary filter. The filter of commonly assigned U.S. application Ser. No. 11/888,929, filed Aug. 3, 2007, discloses a modification to the filters of the '429 patent to further facilitate removal if used as a temporary filter. This is achieved by providing spacers at an end of the filter.
It would be advantageous to provide a filter with improved spacers to keep the retrieval end spaced from the vessel wall to thereby further facilitate removal of the filter.